This invention relates to a baler for forming cylindrical bales (commonly referred to as a "cylindrical" or "round" baler).
Such balers are well known and comprise a bale forming chamber defined by a plurality of belts or chains supported on a plurality of transverse rollers. A bale is formed inside the chamber by driving the belts to roll up in spiral fashion the crop material such as forage or hay gathered from the ground during the advance of the baler. Typically, such bales are bound inside the bale forming chamber before being discharged on the ground. The binding operation is typically carried out by wrapping a twine spirally around the exterior of the bale. The wrapping of the twine is controlled by a twine guiding member which is displaceable transversely of the direction of the travel of the baler in front of the opening for infeeding crop material into the bale forming chamber. The end of the twine is caught by the rotating bale in the chamber and is withdrawn from a storage compartment such as a twine box provided on the chassis of the baler. Due to the tranverse displacement of the guiding member, the twine forms helical turns around the bale to insure the binding over the entire length of the bale.
The guiding member may be constituted by pivotally mounted arm or an arm which is linearly displaceable in front of the opening for crop material into the bale forming chamber.
During the wrapping operation, the infeeding of crop material into the bale forming chamber must be stopped as the chamber is being used in the wrapping operation. To reduce the wrapping time and, therefore, increase the productivity of the machine, it has been proposed in U.S. Pat. No. 3,064,556, U.S. Pat. No. 4,158,331 and European Patent Application 0 041 444 to provide a twine guiding member with two arms which are pivotally mounted and simultaneously displaced over respective paths one-half width of the bale chamber opening. Each arm guides one piece of twine into the bale forming chamber. In this way it is possible to cut the binding time approximately in half compared to a twine wrapping apparatus with a single twine guide arm for transversing the entire width of the bale forming chamber opening and for providing twine wrap spacing of equal distance on the bale.
In the apparatus disclosed in the patent literature listed above, each piece of twine is guided by a separate arm. Thus there is a potential risk that a bale will be defectively bound if one of the twine pieces is not engaged with the bale at the initiation of the wrapping operation. When this happens, only one half of the bale is wrapped and the wrapping operation must be repeated to assure bale integrity when the bale is ejected onto the ground.
In prior art wrapping apparatus with two twine guiding arms, the arms are usually pivotally mounted at spaced locations and in the wrapping operation are moved transversely of the baler in opposite directions. The pivotal mountings of the arms may be located close to the sides of the baler or alternately close to the longitudinal medial axis of the baler. Consequently, it is necessary to provide a drive mechanism which is capable of driving the arm simultaneously in opposite directions and is capable of reversing the direction of pivotal movement of the arms midway of the path of movement. These requirements complicate the design of the drive mechanism and increase the risk of a malfunction in severe operating conditions such as are encountered by this type of agricultural equipment.